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Date: Sun, 9 Sep 2007 16:47:54 +0100
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [kvm-devel] [Qemu-devel] Re: expose host CPU features to guests
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To: Avi Kivity <avi@qumranet.com>
Cc: kvm-devel <kvm-devel@lists.sourceforge.net>, Paul Brook <paul@codesourcery.com>, qemu-devel@nongnu.org

Avi Kivity wrote:
> >I agree. If the host OS has disabled a feature, it's a fair bet it's done 
> >that for a reason.
> 
> The reason may not be relevant to the guest.

For most guests the relevant features are those which work correctly
and efficiently on the virtual CPU.

If the host OS has disabled a feature, most often that's because the
feature doesn't work on the specific host CPU model, but not always.
It might be emulated well, but probably not efficiently.

In some cases, you might want a guest to see features supported by the
host CPU which the host OS has disabled, but I imagine those are
unusual - it doesn't seem very likely.  Can you give an example?

They can be enabled explicitly by the -cpuid flag if needed.

-- Jamie